Thin-film treatment of high-value glycol and amine solvents to remove contaminants

ABSTRACT

A method for cleaning a contaminated solvent used to treat a gas stream, for example a contaminated glycol or a contaminated amine stream, by vacuum evaporation using a mechanically-maintained horizontally-orientated thin film evaporator, where the contaminant material is recovered from the thin film in solvent-free form, as either a heavy organic material or as free flowing salts.

This application claims priority as a continuation in part to U.S.provisional application No. 61/850,544 titled THIN-FILM TREATMENT OFGLYCOL TO REMOVE WATER AND SALTS filed on Feb. 19, 2013.

FIELD OF THE INVENTION

The invention relates to a method of removal of salts and contaminantsfrom a glycol stream, an amine stream, or a mixed stream of one or moreselected solvents by utilizing a horizontally-orientated mechanicallymaintained thin film evaporator operated at modest temperature andabsolute low pressure, thereby forming a dry film of salt contaminantsand/or solid contaminants within the thin film evaporator, wherein saidcontaminants are substantially solvent free and are in the form offlowable solids or a tar-like substance, and recovering thesubstantially contaminant-free glycol and/or amine.

BACKGROUND OF THE INVENTION

Certain solvents are used in industry to scrub gases. These solventsmust be routinely cleaned and re-used. There are two general classes ofsolvents—chemical and physical. Chemical solvents react with impurities,while physical solvents remove impurities due to the solubility of theimpurities in the solvents. Generally, pot distillation, ion exchange,and/or chemical treatments have been used to treat (reclaim) solventsafter the solvent effectiveness is reduced. Solvents particularlyneeding reclamation include ethylene and/or propylene glycols, certainamines including alkanolamines, propropylene carbonate, NMP, as well asproprietary solvents such as di-alkyl ethylene and/or propylene glycols(of which Selexol, a mixture of the dimethyl ethers ofpolyethyleneglycol, is included). Certain solvents, such as Selexol,Sulfinol, and the like, are purely physical solvents, while certainchemical solvents such as ethanolamines react with impurities in thegases.

Similarly, there are three general classes of impurities which build upin the solvents. These include salts, solids, and heavy hydrocarbons.

After use, it may contain, in addition to water and glycols, specificcontaminants according to origin and field of use. Glycol is often usedto remove water from gas streams, and control hydrates in multiphasetransmission pipelines. Further, large amounts of liquids containingglycol, especially ethylene glycol, are obtained in the manufacture ofpolyesters, especially polyester fibers; these liquids also contain, inaddition to water, other impurities stemming from the process. Glycolstreams, which include (poly)ethylene glycol, (poly)propylene glycol,(poly)ethylene/propylene glycols, and the like, typically contain water,solids, dissolved organic contaminants, and dissolved inorganiccontaminants which are usually ionic. The glycol streams must beregenerated.

Large amounts of amine are used industrially. After use, it may contain,in addition to water and amine, specific contaminants according toorigin and field of use. Amines, particularly alkanolamines, are used toremove acid gases from gas streams. Amine streams, which includealkanolamines such as monoethanolamine, diethanolamine,methyldiethanolamine, diisopropylamine, and aminoethoxyethanol,typically contain water, solids, dissolved organic contaminants, anddissolved inorganic contaminants which are usually ionic. The aminestreams must be regenerated. Ion exchange or chemical precipitation areknown methods of removing ionic components including salts, but these donot remove non-ionic organics. The constituents removed by ion exchangeare typically characterized as amino acids and inorganic and organicsalts which are formed in a petrochemical processes or are introduced inthe gas treatment train process. When isolated as pure substances atroom temperatures, these amino acids and salts are solids and are watersoluble. These constituents are effectively removed by ion exchangeprocesses at the expense of large volumes of easily treated waste brinewater. The removal may be less than optimum and the introduction ofwater during treatment is often an inefficiency. Because theseconstituents are solids with high melting temperatures, vacuumdistillation can also remove them by a very inefficient process ofboiling of liquids. The distillation process is inefficient due tofouling of heat transfer surfaces, as well as additional solventdegradation due to the long exposure to heat and reactions between thesolvent and impurities. Amine solvent may undergo degradation, wherebyundesired degradation products are formed in the liquid phase. Thesedegradation products, known as heat stable salts or heat stable aminesalts, may accumulate in the circulating absorbent stream. For aminestreams, the constituents not removed by ion exchange are chemicalproducts of dehydration or reaction with carbon dioxide. This class ofchemical substances can contain diamines, triamines, urea, esters and amyriad of other named and unknown chemical species. These species, whenisolated at room temperature, can be solids; semi-solids; or viscousliquids and do not tend to exhibit significant ionic behavior whendissolved in water.

For glycol streams, particularly monoethylene glycol commonly employedto dehydrate natural gas as an initial step after gathering and prior tofurther processing, the process causes the glycol to absorb water and inthe process become contaminated with naturally occurring andcorrosion-generated salts. The glycol has to be dehydrated prior tobeing recycled in the natural gas production process. The glycoldehydration process is a type of distillation where the absorbed wateris removed by heating and refined in a distillation column. The heatsource in this process is a reboiler that applies the heat to a hotglycol at the bottom of this column contaminated with the salts andcorrosion products resulting in a fouling condition. Use ofstraightforward distillation to remove water is known. However,distillation can result in hot temperatures for long durations, andvarious organics and inorganics in the glycol stream tend to react withone another and with the glycol to form undesirable byproducts. Cleaninga glycol stream with a Kettle Reboiler Reclaimer results in high solventloss due to degradation. Frequent cleanout is required for reclaimer towork. This process is ineffective or in-operative in removing certainionic components, particularly chlorides. The contaminant accumulates inreclaimer and in the circulation of the system until removed by ascheduled cleanout. Alternatively, kettle reboiling can be combined witha second ion exchange process to remove chlorides from systems withthese reclaimers.

Vertically-oriented thin film evaporators have been used to evaporatecertain selected solvents, where the thin film evaporators have platesorientated in a vertical direction, where a thin film of solvents flowsover plates to speed up the process of evaporation of the solvent. Thethin film may be mechanically agitated. Residual solvent carrying theimpurities flows to the bottom of the plates where this material isdisposed of or additionally reclaimed. Deficiencies include high solventlosses due to liquid (solvent) hold up in the vessel, bearing problems,thinning of the film, and slurry buildup caused by excess solvent in thebottoms is difficult to control. The contaminant removed is typicallyhigh in solvent content, typically having at least 15 wt % or moresolvent.

Evaporation is a single-step in a distillation process, such asreboiling liquids in the bottom of a distillation column. Evaporationoffers the possibility of removing all but a small fraction of bothclasses of undesirable constituents from contaminated amine solutionsand salts from glycols in a single processing step. Evaporation inconventional evaporators has met with varying degrees of success due tothe increased fouling of the heat transfer surfaces by the verycontaminants the process was attempting to remove.

It is known to remove undesirable contaminants by vacuum distillation.In this process, water is typically removed first, and then the glycolitself is distilled off, leaving heavy organics and solids. Thisdistillation process is not only effective on undesirable constituentsthat are not ionic in nature and cannot be removed by ion exchange, butalso can remove the class of undesirable constituents that can beremoved by ion exchange. The major drawbacks to the distillation processare poor heat transfer, degradation of heat transfer capability, theprocess necessity to waste significant quantities of the amines andglycols and for amines, their further degradation in the reclaimer.Further, distillation is typically a batch process, which is more laborintensive than steady state processes.

Forced Circulation Evaporator is also a process to clean solvents.Again, deficiencies include high solvent loss due to liquid hold up inthe vessel and slurry build up in reclamation circulation. Further, thebottoms of such evaporator systems have high solvent content from 30 to70 wt % depending on when the system is purged, resulting in asignificant amount of solvent lost as the contaminant level is increased(from 3 to 20 wt %). This process is not considered commerciallyfeasible.

SUMMARY OF THE INVENTION

The invention in a first embodiment provides a steady-state method oftreating a contaminated solvent stream, the process comprising: a)providing a first stream of contaminated solvent comprising an amine, aglycol, or mixture thereof, and one or more contaminants comprisingsalts, organics, solids, or mixtures thereof typically salts and/ororganic material; b) forming and mechanically maintaining a thin film ofcontaminated solvent disposed on a substrate surface at sub-atmosphericpressure, said thin film having a thickness, wherein the thin film isrepeatedly wiped to maintain a film thickness and to move the film alongthe substrate surface; c) recovering a tops vapor phase comprising thesolvent, wherein the concentration of contaminants in the recoveredsolvent is substantially reduced from the concentration of contaminantsin the first stream, and d) recovering a bottoms phase from thesubstrate surface, wherein the bottoms phase recovered from thesubstrate surface comprises contaminants and is a flowable solidmaterial or a tar-like material, said bottom phase comprising less than20% by weight solvent. The first stream is a feed stream. Advantageouslythe bottoms phase recovered from the substrate surface comprises lessthan 10% by weight solvent, and more preferably the bottoms phaserecovered from the substrate surface comprises less than 5% by weightsolvent. Most preferably the bottoms phase recovered from the substratesurface comprises less than 1% by weight solvent, which can in manylocations allow the waste to be treated as non-hazardous material.

In another embodiment of the invention, the first stream of contaminatedsolvent comprises a glycol solvent and contaminant salts, and thebottoms phase recovered from the substrate surface is a flowable powder.Advantageously the bottoms phase recovered from the substrate surface isa flowable powder containing substantially no glycol. In preferredaspects of this invention, the tops vapor phase comprising the solventis condensed to recover the glycol, wherein the glycol loss is 5% byweight or less, preferably 1% by weight or less, based upon solvent massbalance. Advantageously the recovered contaminants have 10% by weight orless of solvent, more preferably 5% by weight or less of solvent, forexample 1% by weight or less of solvent. Alternatively, the tops vaporphase comprising the solvent is condensed to recover the glycol, whereinthe glycol recovered is 95%, more typically 99%, by weight or more ofthe glycol in the first stream, based upon solvent mass balance, andwherein the recovered contaminants have 10%, more typically 5%, byweight or less of solvent. By glycol we mean a solvent which comprisesor consists essentially of a glycol, for example wherein the glycol isselected from ethylene glycol, propylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, polyethylene glycol,polypropylene glycol, polyethylene/propylene glycols, methyl ethers ofpolyethylene glycols, methyl ethers of propylene glycols, and mixturesthereof.

In another embodiment of the invention the first stream of contaminatedsolvent comprises an amine solvent and contaminants and also comprisescontaminant organics and/or contaminant thermally stable salts. The mostimportant amine solvents are alkanolamines, and specifically includealkanolamines selected from the group consisting of monoethanolamine,diethanolamine, triethanolamine, 2-(2-Aminoethoxy)ethanol, methyldiethanolamine, di-isoprpanolamine, Flexsorb™ proprietary alkanolamine,Cansolv™ proprietary alkanolamine, and mixtures thereof. In thisembodiment, advantageously the bottoms phase recovered from thesubstrate surface is a tar-like material which contains 20% by weight orless of solvent, for example 10% by weight or less of the solvent. Thesolvent may comprise or consist essentially of an amine, by which wedefine amines to include functional amines such as alkanolamines, andadvantageously the tar-like material recovered from the substratesurface comprises 5% by weight or less of the amine and/or 5% by weightor less of the solvent. In a preferred embodiment of the invention, thetops vapor phase comprising the solvent is condensed to recover thesolvent, and the solvent loss is 5% or less, preferably 1% or less, byweight based upon solvent mass balance, and wherein the recoveredcontaminant material comprises 10% by weight or less of solvent.Alternatively, the tops vapor phase comprising the alkanolamine iscondensed to recover the alkanolamine, wherein the alkanolaminerecovered is 95%, more typically 99%, by weight or more of thealkanolamine in the first stream, based upon solvent mass balance, andwherein the recovered contaminants have 10%, more typically 5%, byweight or less of alkanolamine.

In another embodiment of the invention, the tops vapor phase comprisingthe solvent is condensed to recover the glycol, wherein the glycolrecovered is 99% by weight or more of the glycol in the first streambased upon solvent mass balance, and wherein the recovered contaminantshave 5% by weight or less of solvent.

Such solvent recovery and recovery of the contaminant material from thethin film is not readily possible with vertical thin films, even ifmechanically maintained, because downward flow caused by gravity resultsin greater levels of solvent in the recovered bottoms. Advantageouslyfor the various aspects of this invention the substrate surface is asubstantially horizontal plane or is a cylindrical wall or portionthereof wherein the axis of the cylinder is substantially horizontallyorientated. Advantageously the thin film has a thickness between about 1and about 5 mm, and the thin film is mechanically maintained byrepeatedly being contacted by wipers which provide additionalcontaminated solvent to maintain a film thickness and which move thefilm along the substrate surface. Generally the pressure issubatmospheric, and may be 10 kPa or less, for example 5 kPa or less.

An important aspect of the invention is the removal and recovery of thecontaminant phase as a substantially solvent-free material, whether thismaterial has a tar-like consistency or has the consistency of afree-flowing powder. In the case where the recovered materials aresalts, the material might be handled as a non-hazardous material, whichgreatly simplifies waste handling. Contaminant salts in glycol can berecovered as free-flowing powder, with over 99% by weight of solvententering the process being recoverable from the vapor phase. Contaminantmaterial in amines can be recovered as a liquid or a tar, with over 99%by weight of solvent entering the process being recoverable from thevapor phase. The process uses a mechanically agitated thin filmevaporator, which is advantageously in the form of a horizontal cylinderconfiguration. The process is steady state and can accept high flowrates and short residence time in the evaporator, i.e, residence time in30 to 90 seconds range, resulting in minimal additional thermaldegradation of solvent.

Another embodiment includes a process of treating a contaminated solventstream, for example a contaminated glycol stream or a contaminated aminestream, by a) introducing contaminated solvent to a mechanically-formedmoving thin film on a horizontally orientated heated substrate underconditions of elevated temperature and sub-atmospheric pressure, whereinthe contaminated solvent forms a mechanically maintained thin film onthe horizontally-orientated substrate, or alternatively on a cylindricalwall or portion thereof wherein the axis of the cylinder is horizontallyorientated, b) mechanically moving and agitating the thin film for atime sufficient to remove substantially all the solvent, and therecovered contaminants are recovered in substantially solvent-free form.The thin film can be mechanically maintained by continuous orintermittent wipers passing over the film, maintaining for example afilm thickness of between 1 mm and 5 mm. Solvent, or alternativelyvolatile contaminants, are evaporated under a sufficiently elevatedtemperature and a sufficiently low pressure, where the pressure is lessthan atmospheric pressure (is a vacuum). Countercurrent flow is used,wherein the volatiles (tops phase) moves in a direction opposite thedirection the wipers are moving the thin film material. Alternatively oradditionally, a sparge gas, typically an inert gas, can be used tofacilitate removal of the vapor phase from the evaporator. As usedherein the term “inert gas” refers to a condensable gas that will notreact with the solvent or contaminants under the process conditionsdescribed herein. Steam is a preferred inert gas used in the processesas a sparge gas.

The thin film is advantageously maintained at an absolute pressure ofbetween about 0.1 and 200 kPa, typically between 1 and 50 kPa, usuallybetween 1 and 20 kPa, and for many solvents is advantageously maintainedat between 1 and 10 kPa, for example between 2 and 5 kPa.

Advantageously the substrate or surface on which the thin film residescan be a horizontally oriented cylinder, where the thin film ismaintained on the inside and/or outside of the cylinder. Typically thethin film is maintained on the inside cylindrical wall, so thatcentrifugal force pushes film material against the wall. This evaporatorconfiguration is better able to obtain solid contaminants as dry powderor as concentrated solvent-free form that greatly simplifies wastehandling.

The processes are advantageous to remove contaminants and degradationproducts from a variety of solvents including especially amines andglycols, to remove the majority constituents of interest.

Generally, if the recovered contaminant phase is organic, the materialwill have the consistency of a syrup or tar. The exact consistency willof course depend on the composition of the contaminants. By tar-like wegenerally mean a viscosity at room temperature of greater than 10000centipoise. The consistency of a recovered organic phase is secondary tothe point that the recovered contaminant material is substantiallysolvent-free, having at a minimum 20% or less by weight solvent, morepreferably 10% or less by weight solvent, for example 5% or less byweight of solvent, and in certain cases 1% of less by weight ofsolvents.

Advantageously, the contaminated solvent stream is treated in ahorizontally oriented mechanically maintained thin film treatmentapparatus operating at steady state, and the residual recoveredcontaminants contain less than 10%, for example 5%, of the solventoriginally introduced to the reclamation process, and advantageouslycontain less than 1% of the solvent originally introduced to thereclamation process. Multiple passes may be required to remove bothvolatile and non-volatile contaminants, if it is desired to removecertain contaminants that are more volatile than the solvents, as wellas to remove certain contaminants that are less volatile than thesolvent. Traditional vertical thin films are typically limited to 20% ormore of the solvent originally introduced to the reclamation processbeing in the resulting contaminant stream. Waste composition of salt orother contaminants in the described inventions will typically have from20 wt % or less solvent.

A horizontal-axis wiped film thermal evaporator can remove contaminantsfrom certain solvents. By horizontal we mean a substantial portion ofthe flat substrate supporting the thin film, or more typically asubstantial portion of the cylinder or cone whose wall supports the thinfilm, is substantially horizontal. The orientation of a cone or cylinderis the orientation of the axis thereof. While a preferred orientation ishorizontal, in less preferred configurations the substrate can besomewhat off horizontal, for example forming an angle of 30 degrees orless from horizontal, preferably less than 10 degrees from horizontal.

As is known in the art, the thin film is mechanically maintained byperiodic wipers, said wipers re-establishing the thin film and alsopreventing localized dry spots leading to fouling and “burn-on;” whichare typical problems with normal distillation processes. Said wipersmove an excess of material which forms the thin film before the wiper,so that the thickness of the film can be maintained. An important aspectof the horizontally oriented mechanically maintained thin filmevaporator is that, unlike vertically oriented evaporators, there is nobottom “steady” bushing that would otherwise need continuous lubricationand flushing. Generally, the recovered contaminant streams, be theyheavy hydrocarbons, hetero-molecules, or salts, are sticky, abrasive,and corrosive. Maintaining a bushing in contact with such verticallyoriented substrate material is an operational problem where potentialsolutions, e.g., flushing a bottom bearing with solvent or withlubricant, results in lower recovery efficiency, increasing thecontaminant load, or both.

The horizontally-orientated wiped thin film evaporator has movingcomponents, often called wipers, which when driven over the thin filmfacilitate evaporation at the surface wall due to mechanical shear andheat at the wall. By “wall,” “substrate,” or “evaporating substrate” wemean the surface on which the thin film resides during the evaporation.Wipers or blades are maintained a fixed small distance from theevaporating substrate, and these wipers or blades are operative toredistribute and/or move the evaporating film of solvent andcontaminants along the face of the evaporating substrate. By periodic wemean the wipers move over the surface of the thin film at least onceevery 10 seconds, and typically a wiper will move over a given surfaceof the thin film multiple times per second, and generally at significantvelocity, for example 20 to 75 ft/sec. The horizontal forced circulationimparted by wipers in preferred embodiments does not have significantliquid holdup, but contains sufficient contaminated solvent to allowwetting the covered surface area, said liquid before the wiper beingpushed forward by sheer force of the wiper.

The vertical wiped film evaporator used in the art may more typicallyhave liquid hold up so that the solvent can be evaporated by mechanicalshear at the wall, conductive heat from the wall and heat of the bulksolution in the bottom. The forced circulation evaporator has similarheating requirements of from the bulk solution heating the inlet feed.

In another embodiment, the invention includes a process of treating acontaminated glycol stream, by mechanically forming a moving thin filmon a heated substrate under conditions of elevated temperature andsub-atmospheric pressure, wherein the residence time on the thin filmevaporator is sufficient to remove substantially all the glycol stream,respectively, and the recovered ionic material is stored at reducedpressure, such that the recovered ionic contaminants are recovered indry powder form. The thin film is mechanically maintained by continuouswipers to a thickness of between 1 and about 5 mm, for example about 2to 3 mm, thickness. The unit advantageously dries the thin film suchthat the residual contaminants, which are primarily salts, are recoveredas free flowing powder. This obtaining of the contaminant salts, and thelike, as powder greatly simplifies waste handling.

In another embodiment the process advantageously removes contaminantsand degradation products from amines and glycols used by refinery,natural gas and petrochemical processes, wherein a single treatment mayremove the majority of contaminants of interest. Solvent waste is lowerthan other vacuum distillation reclamation technologies, and the processsaves the disposal and minimizes environmental impact. The inventionreduces waste and increases life span of the fluid and potentiallyreduces corrosion of system metallurgy.

The horizontal wiped film evaporator is advantageously used in place ofcommercially available kettle horizontal reboilers or other vacuumdistillation techniques including vertical wiped film evaporators.

The solvent loss is lower than any other known vacuum distillation, andis typically 5% by weight or less, more typically 1% by weight or less,of solvent loss based upon solvent mass balance (total solvent recoveredversus total solvent in contaminated feed) for rapid commercialprocessing.

The processes are advantageously to remove contaminants and degradationproducts from amines used by refinery, natural gas and petrochemicalprocesses to remove certain contaminants, including acid gases. Othertechnologies require further processing of the waste stream, higher lossof solvent, or both. When amine is processed a tar like bottoms phase isobtained, and when physical solvents like Selexol™ are processed theresulting contaminant is in liquid bottom phases. While conditions canof course be selected to obtain wet bottom phases, for example wet saltswhen processing glycol, in a preferred embodiment waste composition ofsalt or other contaminants will have from 20 wt % or less solvent on adry basis or will be substantially dry.

Another embodiment includes a process of treating a contaminated aminestream, or alternatively treating a contaminated Sulfinol™ solvent,which is a blend of a tertiary amine, an alkanolamine orethyl-alkanolamine, and Sulfolane™ (tetramethylene sulfone,tetrahydrothiophene-1,1-dioxide), by mechanically forming a moving thinfilm on a heated substrate under conditions of temperature andsub-atmospheric pressure, wherein the residence time on the thin filmevaporator is sufficient to remove substantially all the amine stream orhybrid amine stream, respectively, and the recovered material arerecovered in dry powder form, or organic contaminants are recovered insubstantially solvent-free form. Heavy hydrocarbon contaminants are alsoreadily removed from the contaminated amine/hybrid amine stream. Thethin film may be mechanically maintained by continuous wipers to athickness of between 1 mm and 5 mm. This obtaining of the contaminantsalts, and the like, as powder or as a dry material, greatly simplifieswaste handling.

Another aspect is an embodiment which includes a process of treating acontaminated Selexol™ solvent, which is a blend of compounds, bymechanically forming a moving thin film on a heated substrate underconditions of temperature and sub-atmospheric pressure, wherein theresidence time on the thin film evaporator is sufficient to removesubstantially all the amine stream or hybrid amine stream, respectively,and the recovered contaminant material is optionally stored at reducedpressure. Heavy hydrocarbon contaminants are also readily removed fromthe contaminated Selexol™. The improvement over prior processes is inthe recovery from the thin film of solvent-free contaminant material.The thin film is mechanically maintained by continuous wipers to athickness of between 1 and 5 mm thickness. The consistency of therecovered contaminants is variable.

The chemical-type gas treating solvents which can be advantageouslytreated with the described process include alkylated propylene glycolsand/or alkylated ethylene glycols, ethylene/propylene glycols (forexample dimethyl ethers of polypropylene glycol, propylene glycolsand/or ethylene glycols, Selexol™, Sulfolane™, Sulfinol™ D, Sulfinol™ M,generic amines, and especially alkanolamines including for examplemonoethanolamine, diethanolamine, triethanolamine,2-(2-Aminoethoxy)ethanol covered under CAS 929-06-6, methyldiethanolamine, di-isopropanolamine, Flexsorb™ proprietary alkanolamine,and Cansolv™ proprietary alkanolamine, as well as propylene carbonate,and N-methyl pyrrilidone. The processes are advantageously used toremove contaminants and degradation products from solvents, such asamines and glycols, used by refinery, natural gas and petrochemicalprocesses to remove the majority constituents of interest. Thesesolvents are used in gas processing and in refineries to remove sour gasand acid gases, and hydrate inhibition (remove water).

By “glycols” we mean alkyl glycols, alkylene glycols,poly-(alkylene)glycols, and alkyl ethers of the foregoing, and otherglycols mentioned specifically herein.

It is also envisioned to utilize a pre-separation technology, especiallywith glycols but also with amines, which can remove a portion ofcontaminants, typically removing volatile contaminants, water, and somesolvent, before introducing the feed stream into the TDSX™ thin filmmechanically agitated evaporator. In particular for glycol, pretreatingwith a forced circulation evaporator to evaporate the water from glycolbefore the thin film evaporator needed to utilize this process isanticipated for many commercial applications.

Another embodiment includes a process of treating to remove certaincontaminants from a contaminated physical solvent, a contaminatedchemical solvent, or a contaminated hybrid chemical/physical solvents,for example a contaminated glycol stream, or a contaminated aminestream, by mechanically forming a moving thin film of the contaminatedsolvent on a heated horizontally-orientated evaporator substrate underconditions of elevated temperature and sub-atmospheric pressure, whereinthe residence time on the thin film evaporator is sufficient to removesubstantially all the solvent, for example the glycol or amine stream,respectively, and the ionic contaminant material or organic contaminantsare recovered in dry powder form and/or organic contaminants arerecovered in substantially solvent-free form for example as a tar orliquid. The thin film is mechanically maintained by continuous wipers toa thickness of between 1 mm and 5 mm.

Another embodiment includes a method of treating a contaminated glycolstream, the process comprising: 1) providing a first stream ofcontaminated glycol comprising glycol, water, and dissolved salts; 2)mechanically forming and maintaining a moving thin film on ahorizontally-orientated heated substrate under conditions of elevatedtemperature and sub-atmospheric pressure, at a pressure of 1 to 10,typically 3 to 5 kPa, and at a temperature of greater than 100 degreesC., for example between 160 to 190, typically 170 to 180 degrees C.(where the temperature range will differ for different solvents),wherein the thin film is wiped to maintain film thickness between about1 to about 5 mm: 3) condensing and recovering the glycol and waterstream, and 4) recovering the salts from the thin film evaporator assubstantially dry powder. By substantially dry we mean the solidscomprise greater than about 50% by weight solids, preferably greaterthan about 80% by weight solids, the remainder being glycol, water, andother contaminants.

Advantageously and importantly, the thin film evaporator apparatuscontains rotors or wipers to continuously form and maintain the thinfilm on a horizontally-orientated substrate. The economic attainment ofsolvent-free contaminant material from a steady state thin film is notpossible unless the thin film is mechanically maintained. A preferredhorizontally orientated substrate is a cylinder, where the axis of thecylinder is horizontally orientated, and it is recognized that asubstantial portion of the evaporating substrate, be it the interiorwall of the cylinder or the exterior wall of the cylinder, may not behorizontally orientated. A commercial embodiment of a preferred thinfilm evaporator is the Artisan® Rototherm E Thin™ Wiped Film Evaporator.The use of the mechanically maintained thin film evaporator, inconjunction with pressures and temperatures known to those of skill inthe art, allows for up to 99% evaporation in a single pass. An exemplaryapparatus can be found at www.artisanind.com/ps/equipment/rotothermfeatures.html which shows a cross section of a commercially availablehorizontally orientated cylinder type thin film evaporator apparatus. Inthe embodiment shown, the wiper is depicted as maintaining a “bow wave”of material, where this bow wave deposits additional material to replacematerial lost to vaporization, and thus to maintain consistentthickness. The wipers have a body, and in the context of wipers movingin a cylinder, the wiping edge of the wipers can be called a rotorblade. While the figure shows text indicating that the wipers move at 30to 60 feet per second, any appropriate velocity can be used. The ArtisanIndustries' Rototherm™ is a specialized evaporator which uses ahigh-speed rotor that creates centrifugal force, which keeps the feedagainst a heated horizontal cylinder wall. A turbulent thin film betweenthe rotor blades and wall covers the entire heated surface. Theturbulent thin or wiped film creates high heat transfer efficiency,minimizing the area required for evaporation. The film is continuouslyrenewed by the incoming feed as the progressively more concentratedmaterial moves towards the bottoms discharge nozzle. Product residencetime in the Rototherm™ is generally measured in seconds, minimizingdegradation of heat-sensitive materials.

The use of a wiper to maintain the film thickness is highly beneficial,as the viscosity and other properties of the liquid change considerablyas the glycol, or amine, is quantitatively removed. Further, fouling issubstantially reduced.

Preferred operation for glycol is at a pressure of 1 to 10, typically 2to 5 kPa, at a temperature of 160 to 190, typically 170 to 180, degreesC. This process is optimally operated at approximately 2 kPa absolutepressure in order to obtain a discharge of dry flowable solids.

Typical thin film evaporators are the known vertical wall, where thethin film is maintained by flow due to gravity. Such a process is notuseful for this invention, as this type of thin film cannot toleratehigh solids loading as will be experienced as the amount of glycol oramine removed approaches 99%. Further, the use of the mechanicallymaintained thin film provides agitation and turbulence, therebyincreasing efficiency. Surprisingly low temperatures are needed, socontaminants formed at higher temperature distillation will not form inthe process of this invention. Other advantages of this mechanicallyformed and maintained film include ability to handle changing and veryhigh viscosity (up to 2 million centipoise); negligible pressure drop;High turndown ratio (10:1 or better); High surface to volume ratio, afully wetted wall at all evaporation and flow rates where the thin filmis unaffected by gravity; and no dry spots and minimal to no fouling.Generally a wiper maintains a “bow wave” of material, where this bowwave deposits additional material to replace material lost tovaporization, and thus to maintain consistent thickness, and constantlyrenews the material at the heat transfer surface. The wipers have abody, and in the context of wipers moving in a cylinder, the wiping edgeof the wipers can be called a rotor blade.

Particularly useful applications for this technology include: AmineSolutions—removal of heat stable salts and other degradation productswhere minimization of wastes or rinse water is required, or removal ofdegradation products which cannot be removed by ion exchange technology,e.g., THEED (tris-hydroxyethylethylenediamine); Glycol Solutions—removalof salts and corrosion products from natural gas processing plant'sdehydration systems; Sulfolane™ Extraction Solvent—removal ofcontaminants and degradation products from systems which extract cyclicfrom non-cyclic organics in refinery recovery streams; andSelexol™—removal of contaminants and degradation products.

EXAMPLES

A horizontal, mechanically aided thin-film Rototherm™ evaporator wasused for these examples unless otherwise specified.

Contaminated glycols when fed into the thermal horizontally orientatedwiped film evaporator returned clean glycol condensed from the tops andsubstantially dry flowable salts and other solids from the bottoms.Slurries of salts can also be obtained, including slurries of salts andliquid contaminants or slurries of salts in solvent.

The following discussion relates to treatment of amines, but is alsoapplicable for treatment of glycols. In one embodiment tested with anamine stream, stripping steam was introduced through a critical flownozzle on selected runs in order to completely sweep the bottomsmaterial of valuable amines thereby increasing recovery. Once the liquidfeed entered the Rototherm shell, the water and amines were removed fromthe feed by turbulent liquid thin-film evaporation as the feed flowedalong the inner sidewalls of the Rototherm™ jacketed process section.The concentrated bottoms stream exited the mechanical thin filmevaporator by gravity into a 1-gal glass jar. The water and aminesevaporated from the feed exited the Rototherm™ through the 4″ vaporoutlet, traveling through a vapor body and then to a condenser where thewater and amines were condensed and labeled as Distillate. The ventstream from the condenser then entered a cold trap cooled with dry ice,immediately upstream of the vacuum pump, which was installed to catchany remaining condensable exiting the condenser. All output streams(bottoms, Dl distillate, and cold trap distillate) were collected inglass jars that were periodically isolated from the process and changedout as needed.

Pilot Plant Degraded Amine Feed Characterization Feed Sample Water, wt.% DEA, wt. % THEED, wt. % HSS, wt. % 1000 65 27 5 3 2000 67 28 5 0 300069 28 2 1

A pilot plant test was performed on various amine streams. Note: Allsamples were pretreated to remove hydrogen sulfide and enough causticadded to free the amines for recovery. The first feed containedapproximately 5% THEED, 65% water, 27% amines and the balance salts asdescribed above. This feed was not pre-treated to remove any of thesalts. The second feed was similar in composition to the first but thefeed was pre-treated to remove some of the salts. The third feedcontained approximately 2% THEED, 70% water, 28% amines and the balancesalts. This feed was not pre-treated to remove any of the salts.

Typically amine is run with the thin film maintained at between 148.88degrees C. and 232.22 degrees C., and at a pressure (absolute) ofbetween 0.133 and 13.33 kPa, advantageously between 0.67 and 3.33 kPa.The steam-sparged mechanically maintained thin film evaporatorsuccessfully recovered DEA from all of the feed materials that wereprocessed with liquid recoveries ranged to 99.8% when operating atconditions near the optimal, vacuum of 1.33 kPa and film temperaturesfrom 174.44 degrees C. to 212.78 degrees C. These temperatures varydepending on concentrations of THEED and heat stable salts in thedegraded amine feed.

Based on the observations and results of the amine tests, the processeffectively removed inorganic salts, non-volatile heat stable salts, andup to 60% of the liquid THEED entering with the degraded DEA feed in asingle evaporation step. The other liquid degradation product is knownas bis-HEP. It was only recovered at 15% of that incoming with the feed.The pilot plant test processed three different contaminated aminefeedstocks, and effectively recovered up to 99.8% of the diethanolamine(DEA) in the feed, while discharging a concentrated bottoms streamconsisting of heat stable salts, Tris(hydroxyethypethyelendiamine(THEED), Bis(hydroxyethyl)piperazine (bis-HEP), and trace residual DEAand uncharacterized organic material. The degraded DEA solutions treatedin the mechanically maintained thin film evaporation process recovered98+% of the incoming DEA and water while removing 60% of the undesirableTHEED and 15% of the bis-HEP plus all heat stable and inorganic saltsfrom the feed solution in a single step. The pilot process ran steadilyduring the amine pilot trial and there were no signs of fouling oraccumulation of solids or concentrated material on the jacketed walls ofthe evaporator. A steam sparge through the thin film evaporator isrequired to maximize DEA recovery. Without steam sparge the DEA recoverywas limited to approximately 87%, but a feed to sparge rate ratio of14-21 weight per weight yielded greater than 95% DEA recoveries. Whilesparge gas can be any inert gas, steam is preferred to simplifycondensation of the vapors.

The concentration of THEED in the feed material affects the optimumoperating temperature required to maximize DEA recovery. For the feedcontaining 5% THEED, an optimum film temperature of approximately 210degrees C. was required to achieve greater than 95% recovery. With afeed containing 2% THEED, the film temperature of approximately 173.89degrees C. was sufficient, at an operating pressure of 1.33 kPa.

The material balances performed on the pilot plant runs identifysignificant and previously unidentified degradation products in thedegraded amine solutions, Depending on the processing conditions and thesource for feed, the removal of those constituents ranged from 40% to84%.

A pilot plant test was performed on a contaminated glycol stream. Sampleidentifiers and characteristics are shown below.

Pilot Plant Salt Degraded Glycol Feed Characterization Feed SampleWater, wt. % MEG, wt. % Salts, wt. % 4000 81.7 15 3.3 5000 9.6 88 2.46000 0 90 10

Based on the observations and results of both tests, the pilot planteffectively removed inorganic salts from the glycol water solutions. Thesalts were discharged as a free-flowing dry powder while all the glycoland water was recovered as a salt-free solution ready for reintroductioninto the natural gas process. The dilute MEG solution in feed sample4000 typifies a very weak glycol solution without benefit ofpre-evaporation of the incoming water prior to being fed to the thinfilm evaporator. This is an example of MEG highly diluted with producedwater and salt. The concentrated MEG solution in feed sample 5000represents one of a dilute solution subjected to pre-evaporation of themajority of the water before being fed to the thin film evaporator. Thiswould be typical of a MEG mixture withdrawn from MEG regeneratorreboiler. The concentrated MEG solution in feed sample 6000 representsone of a preevaporated regenerator reboiler solution with the waterremoved and including salts precipitated during the evaporation stepbefore being fed to the thin film evaporator as slurry. This would betypical of concentrated mixture withdrawn from MEG regenerator reboiler.

Another Example was run on contaminated Sulfolane™. Sulfolane™ isdifficult to clean with ion exchange. Contaminated Sulfolane™ wasobtained from a petrochemical plant. In order to model the wipe filmevaporator, 175 mL of the contaminated Sulfolane™ sample was mixed with35 mL of distilled water and placed in a distillation flask. The samplewas stirred, heated and a vacuum applied. A first fraction was distilledat 58 degrees C. and 15.99 kPa; it is believed that this fraction wasmostly water. A second fraction was distilled at 185 degrees C. and apressure of 7.33 kPa. The contaminated sample was black and dirty inappearance. The distilled sample was nearly water white and free fromparticles. The bottom fraction from the distillation was a black tarthat solidified at room temperature.

Another Example was run with contaminated Selexol™. A dark, contaminatedsample of Selexol™ was obtained from a commercial solvent reclamationcompany. Initial analysis suggested the sample contained about 69% (all% by weight) Selexol™, about 6% water, and about 26% unidentifiedorganic contaminants. The contaminated material was passed through ahorizontal wiped film evaporator under conditions to remove water, thatis, at about 212.78 degrees C. and 13.33 kPa absolute pressure. Thematerial separated from the contaminated stream contained 60% water and40% Selexol™. The “bottoms” contained about 70.6% Selexol, about 30%unidentified organic contaminants, and no water. This bottoms sample wasthen run a second time through a horizontally orientated mechanicallywiped film evaporator, under conditions to remove organic contaminants,that is, 223.89 degrees C. and 1.33 kPa absolute pressure. In thissecond run, Selexol™ is recovered and condensed, and the bottoms arecontaminants. When run at 257.78 degrees C. and 0.67 kPa absolutepressure, the recovered solvent was substantially clear and containedabout 81% Selexol™ and 19% unidentified hydrocarbons, and the bottomscontained about 30% Selexol™ and 70% organics. When the same sample wasrun at 223.89 degrees C. and 1.33 kPa absolute pressure, the recoveredsolvent was clear and contained about 98% Selexol™ and 2% unidentifiedhydrocarbons, and the bottoms contained about 50% Selexol™ and 50%organics.

The THP (total petroleum hydrocarbons) concentrations were monitored.THP values in the initial feed were 129 ppm (parts by million byweight), and a substantial portion of this (102 ppm) could be found inthe first tops to remove water, leaving about 90 ppm in the bottoms.During subsequent runs to remove organics, the THP differentiated withthe contaminant-containing bottoms having about twice the THPconcentration as the recovered Selexol™ from the tops, e.g., 60 to 70ppm in the tops compared to 120 to 140 ppm in the bottoms. Acetate, atan initial concentration of 18 ppm in the contaminated Selexol™ feed,was totally removed in the dewatering stage, and the acetate stayed withthe aqueous phase. Sodium and calcium present in the originalcontaminated Selexol™ feed were reduced, though at the very lowconcentrations present it is difficult to quantify, with sodium, iron,and calcium each being reduced by half or more, based on theconcentration in the incoming feed compared to the concentration of therecovered cleaned Selexol™.

There were a number of pilot plant tests performed. At film temperatureof 148.89 degrees C., the system separated and recovered only a smallfraction of the Selexol™ present. At pressures above 1.60 kPa, thesystem operated at low efficiency. At pressures of 0.67 kPa andtemperatures of 223.33 to 257.78 degrees C., the Selexol™ recoveryincreased to between 65 and 82% recovery. At 0.27 kPa and temperaturesof 223.33 to 257.78 degrees C. Selexol™ recovery increased to between90% to 99% of the Selexol™ in the original feed.

It is clear that the process can be tailored to meet clientspecifications on recovered product. The remaining bottoms can be runagain to further separate the Selexol™ from the unidentifiedhydrocarbons. It is shown that sometimes two passes through thehorizontally orientated wiped film evaporator may be required, the firstto remove light components and the second to remove (and re-condense andcollect) the solvent from heavier contaminant components.

The contaminants recovered, and the physical state of the recoveredcontaminants, depends on the nature of the solvent and the contaminants.For glycol streams, water can be removed if desired in a first pass, anddry salts are recovered in the bottoms of the final pass through thehorizontally orientated wiped film evaporator. With amines, therecovered bottoms are tarry with little solvent. With Selexol, therecovered solvent stream from the tops contains about 80 to 98% byweight Selexol and from about 20% to 2% unidentified organics, and thebottoms contain more than 50% unidentified organics.

Monoethylene glycol (MEG) Reclamation consists of removal of the salts,corrosion compounds, and other heavy compounds that end up in the MEGafter MEG Regeneration. The salts build up unless removed, and when theybuild up to critical levels while containing acids, they become verycorrosive. The combination of salts, corrosion products, and asphaltinescreate tremendous fouling problems for the reboiler on the regenerator.Pilot plant tests demonstrated excellent continuous dry salt dischargefrom a Rototherm™ pilot unit under all feed conditions, a) dilute saltand glycol, b) 80% MEG and water saturated with salt, and 88% MEG with12% crystallized salt. The obtaining of free-flowing dry salts from thethin film evaporator treating a glycol stream was an unexpected result.

More than one evaporation technology may be applied to reclaim amineswith very low vapor pressures. For example, Forced CirculationEvaporation is a known process to clean solvents, where this may be usedin conjunction with the thin film process described here.

We can obtain ultra-high recovery with the wiped film evaporator. Toreclaim amine for streams containing heat stable salts, the operator maychoose the horizontal wiped film evaporator process, recovering bothwater and amines. To reclaim from a stream devoid of HSS, the operatormay reclaim amine using the horizontal wiped thin film evaporatorprocess described here.

Regardless of feed streams treated, the wiped film evaporator requiresutilities and waste disposal support in order to effectively operate.These are: 1) evaporative heating supplied to the evaporating substrateof the evaporator; 2) cooling and/or chilled water supplied to condensethe evaporated recovered components; 3) a vacuum system sufficient insize to maintain at least a 1.33 kPa vacuum on the system includingprocess non-condensables; and 4) an effective removal system forextracting powders, solids, tars and liquids from the evaporator whilemaintaining operating vacuum.

An 85 sq ft TDSX™ horizontally orientated mechanically maintained thinfilm evaporator runs mixtures of water and various amines at differentrates. Heat transfer flux BTU/sq ft/hr varies with the organic contentin a water mixture. The same is true for mixtures of water and glycols.

The thin film is mechanically maintained by wipers. Advantageouslywipers move at a velocity of between 1 and 100 feet per second, withwipers passing over a surface at least once every five seconds or so,preferably between 1 and 10 times per second. Wipers move perpendicularto the product flow, so as to not push untreated product out the exit.If the evaporator surface is the inside surface of a tube, rapidspinning of wipers in the tube provides centripetal force to force thestream against the evaporator wall. Heat is supplied through the wall.

The invention is meant to be illustrated by, and not limited to, theexamples.

What is claimed:
 1. A steady-state method of treating a contaminated solvent stream with a horizontal thin film evaporator having a heated substrate surface, the process comprising: a. providing to the horizontal thin film evaporator a feed stream of contaminated solvent comprising i. an amine, a glycol, or mixture thereof, wherein the amine comprises one or more alkanolamines and ii. one or more contaminants comprising salts, organics, solids, or mixtures thereof; b. forming and mechanically maintaining a thin film of contaminated solvent disposed on the heated substrate surface at sub-atmospheric pressure, said thin film having a thickness, wherein the thin film is repeatedly wiped to maintain the film thickness and to move the thin film along the heated substrate surface; c. recovering a tops vapor phase comprising the solvent, forming a recovered solvent, wherein the concentration of contaminants in the recovered solvent is substantially reduced from the concentration of contaminants in the feed stream, and d. recovering a bottoms phase from the heated substrate surface, wherein said bottoms phase comprises less than 20% by weight solvent.
 2. The method of claim 1, wherein the bottoms phase recovered from the heated substrate surface comprises less than 10% by weight solvent.
 3. The method of claim 1, wherein the bottoms phase recovered from the heated substrate surface comprises less than 5% by weight solvent.
 4. The method of claim 1, wherein the feed stream of contaminated solvent comprises a glycol solvent and contaminant salts, and wherein the bottoms phase recovered from the substrate surface is a flowable powder.
 5. The method of claim 4, wherein the feed stream is a contaminated glycol stream comprising contaminant salts, and wherein the bottoms phase recovered from the heated substrate surface is a flowable powder containing substantially no glycol.
 6. The method of claim 4, wherein the tops vapor phase comprising the solvent is condensed to recover the glycol, wherein the glycol recovered is 95% by weight or more of the glycol in the feed stream, and wherein the bottoms phase comprises 10% by weight or less of solvent.
 7. The method of claim 4 wherein the tops vapor phase comprising the solvent is condensed to recover the glycol, wherein the glycol recovered is 99% by weight or more of the glycol in the feed stream based upon solvent mass balance, and wherein the bottoms phase comprises 5% by weight or less of solvent.
 8. The method of claim 4 wherein the glycol is selected from ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, polypropylene glycol, polyethylene/propylene glycols, or mixtures thereof.
 9. The method of claim 1, wherein the feed stream of contaminated solvent comprises an amine solvent and contaminants comprising organics and thermally stable salts, wherein the bottoms phase recovered from the heated substrate surface is a tar-like material which contains 20% by weight or less of the amine solvent.
 10. The method of claim 9, where the amine solvent comprises alkanolamines selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, 2-(2-Aminoethoxy)ethanol, methyl diethanolamine, di-isopropanolamine, and mixtures thereof.
 11. The method of claim 9, wherein the tar-like material recovered from the heated substrate surface comprises 10% by weight or less of the solvent.
 12. The method of claim 9, wherein the tar-like material recovered from the heated substrate surface comprises 5% by weight or less of the solvent.
 13. The method of claim 9, wherein the tar-like material recovered from the heated substrate surface comprises 5% by weight or less of the alkanolamine.
 14. The method of claim 9, wherein the tops vapor phase comprising the solvent is condensed to recover the solvent, wherein the alkanolamine recovered is 95% by weight or more of the alkanolamine in the feed stream, and wherein the bottoms phase comprises 10% by weight or less of alkanolamine.
 15. The method of claim 9, wherein the tops vapor phase comprising the solvent is condensed to recover the alkanolamine, wherein the alkanolamine recovered is 99% by weight or more of the alkanolamine in the feed stream, and wherein the bottoms phase comprises 5% by weight or less of alkanolamine.
 16. The method of claim 1, wherein the heated substrate surface is a substantially horizontal plane or is a cylinder wherein the axis of the cylinder is substantially horizontal, and wherein the thin film is mechanically to maintain the film thickness and move the thin film along the heated substrate surface.
 17. The method of claim 1 wherein the sub-atmospheric pressure is 10 kPa or less.
 18. The method of claim 1 wherein the sub-atmospheric pressure is 5 kPa or less.
 19. The method of claim 1 wherein the sub-atmospheric pressure is between 1 and 20 kPa.
 20. The method of claim 1, further comprising a step of introducing a sparge gas above the thin film of step b to facilitate removal of the tops vapor phase from the horizontal thin film evaporator.
 21. The method of claim 20, wherein the solvent comprises one or more alkanolamines.
 22. The method of claim 1, wherein the method comprises: a. providing contaminated solvent to a mechanically-formed moving thin film on a horizontally orientated heated substrate surface under conditions of elevated temperature and sub-atmospheric pressure of between 1-20 kPa, wherein the contaminated solvent forms a mechanically maintained thin film on the horizontally orientated heated substrate surface; and b. mechanically moving and agitating the thin film for a time sufficient to remove substantially all the solvent contained in the thin film, wherein the tops vapor phase moves in a direction substantially perpendicular to the thin film's movement. 